The present invention relates to a scattered light smoke detector.
It is known to design optical smoke alarms as scattered light smoke alarms. The scattered light smoke alarm has either a measuring chamber in which the smoke penetrates through a labyrinth, or is formed as a free light scattered light smoke alarm, wherein a measuring volume is examined in a free space with respect to a reflection on smoke.
Accordingly, it is an object of the present invention to provide a scattered light smoke alarm which is a further improvement of the existing smoke alarms of this type.
In keeping with these objects and with others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in a scattered light smoke alarm which has means for providing a definite measuring volume, said means being formed as means selected from the group consisting of two light receivers, and an imaging optical system for one light receiver.
When the scattered light smoke alarm is designed in accordance with the present invention, it has the advantage in that an improved interference suppression is obtained, since a greater and first of all exactly defined air volume of the particles or smoke density is measured. No clouds, for example cigarette smoke have the smallest influence on the measuring results.
The definition of the measuring volume can be performed by a corresponding optical construction. For this purpose either two receivers are used or a transmitter and a receiver can be utilized each having an imaging optical system of lenses and apertures for definition of the measuring volume. Thereby the interference sensitivity of the inventive scattered light smoke alarm is minimized. The measuring volume is located in a region where in the event of a fire a high smoke density can be expected, and in the event when there is no fire there are low interferences. A typical region for this purpose is substantially 4-10 cm under a space sealing.
It is especially advantageous when the light receiver is composed of at least one detector row and a detector a nay. This advantageously provides for a possibility of measuring a speed and movement direction of an object. Also, this is an effective measure for distinguishing smoke and objects.
It is especially advantageous when each light receiver has two detector rows arranged perpendicular to one another, for two-dimensional tracking of a measuring object. It increases the interference safety and provides a simple design as a whole detector array.
A further advantageous embodiment of the inventive device for distinguishing between smoke and objects is the evaluation of contours of a measuring object. An object has sharp contours, while in contrast smoke has soft transition at the edges of a smoke cloud. By means of an image evaluation, thereby smoke or another object can be determined. This provides for a good possibility of the plausibilizing of the scattered light measuring results.
With the use of two light receivers which are offset relative to one another and include at least one detector row or a detector array, it is possible to determine a distance and a speed of the measuring object relative to the receivers. As a result, a spacial tracking of an object is possible.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.